1. Field of the Invention
The present invention relates generally to a screen plate cleaning station for cleaning dirt adhered to a screen plate which is used for a stencil-type printing system to form printing patterns.
2. Description of the Prior Art
As well known, the stencil-type printing system using a meshed screen plate, which has hitherto been carried out in the printing industry, is contributing to a remarkable advancement in print wiring processing techniques through its application to mounting of electronic components in the field of electronic technology. Particularly, in the field of recent surface mount technology (SMT), a screen plate having a metal mask is used to form fine and close printed patterns composed of solder paste on a surface of a dielectric substrate made of e.g. epoxy resin. The thus formed printed patterns of solder paste are utilized to highly integrate the electronic components such as semiconductor devices or ICs to be mounted on the printed circuit board.
In addition, the field of application of the stencil-type printing system using the above screen plate is farther extended, including formation of resist ink on the dielectric substrate using a mask made of emulsion or resin, and application to printing means for indicating characters or symbols on electronic components with ink. In order to clean such a screen plate, various types of cleaning apparatuses have been proposed.
Referring to FIG. 12 there is depicted a construction of a conventional screen plate cleaning apparatus.
As shown in FIG. 12, the screen plate cleaning apparatus is generally designated at 101 and comprises a conveying mechanism 102, a cleaning vessel 103, cleaning nozzles 131, flashing nozzles 132, a rinsing vessel 104, rinsing nozzles 141, and dehydrating nozzles 142. Reference numeral 105 denotes a screen plate called a screen mask, 106 a cleaning liquid, 107 a rinsing liquid, and 108 a warm air.
The cleaning apparatus 101 shown in FIG. 12 cleans. the screen mask 105 through the following steps (1) to (6).
(1) The screen mask 105 is set in the cleaning apparatus 101. PA0 (2) Power supply is turned on and cleaning conditions are determined. PA0 (3) When the cleaning apparatus 101 is actuated, the screen mask 105 is conveyed to the cleaning vessel 103 by means of the conveying mechanism 102. PA0 (4) The cleaning nozzles 131 vertically move to spray the cleaning liquid 106 at 40.degree. C. An the form of a high-pressure shower onto the both surfaces of the screen mask 105. PA0 (5) After cleaning operation, the flashing nozzles vertically move to blow the both surfaces of the screen mask 105 with the warm air 108 for dig up. PA0 (6) The thus dried screen mask 105 is conveyed to the rinsing vessel 104 by means of the conveying mechanism 102. Through the rinsing step in the same manner, the screen mask 105 is returned to the initial setting position to complete the cleaning. PA0 (1) A screen plate is set in the cleaning apparatus. PA0 (2) A cleaning liquid is fed from a tank to rotational nozzles for spraying the cleaning liquid in the form of a rotational shower onto the screen plate, the cleaning liquid being reservoired inside the cleaning apparatus. PA0 (3) An ultrasonic wave is applied to the interior of the thus reservoired cleaning liquid to perform ultrasonic cleaning while rotating the screen plate. PA0 (4) The cleaning liquid is drawn into another tank and the screen plate is rotated to shake off the adhered cleaning liquid by the centrifugal force. PA0 (5) Warm air is supplied onto the screen plate for drying. PA0 (1) In the case of for example a screen plate fitted with a metal mask, as will be described later, a printing metal mask is attached by an adhesive and via gauze to the inside of a metal frame. Then, using the screen plate fitted with the metal mask, solder paste is printed on the dielectric substrate by means of the stencil-type printing system. PA0 (2) In the prior art, a manual cleaning method was carried out in which the screen plate is cleaned up by hand with a rag infiltrated with 1,1,1-trichloroethane, although the use of this agent was prohibited thereafter from the medical point of view. Another agent could be used in place of the above agent but are poor in cleanability by themselves without using with machine, and are too strong in chemical odor to use them without providing any ventilating device. PA0 (3) In the above two conventional apparatuses, the screen plate is entirely accommodated within the apparatuses so as to allow the cleaning liquid to be sprayed onto the entirety of the screen plate. The latter apparatus in particular is so configured that the screen plate is rotated for ultrasonic cleaning and that the cleaning liquid is shake-off dried by the centrifugal force. This will result in not only increase in size of the apparatus but also increase in the amount of consumption of the cleaning liquid as well as costs of production and maintenance. Above all, the screen plate cleaning apparatus 101 of FIG. 12 is of two-vessel type and is further provided with the conveying apparatus 102, with the result that its maintenance cost and the like is further raised.
Besides, another type of conventional apparatus not shown is also known which additionally employs ultrasonic cleaning in the following steps (1) to (5) using a glycol ether cleaning liquid.
However, the two conventional screen plate cleaning apparatus involve several problems that follows.
On the other hand, the cleaning liquid adhered to the screen plate during the cleaning step will mostly volatile by virtue of the warm air in the drying step. However, a part of the cleaning liquid may remain left as it is for the time being as a result of infiltration into gaps at adhesive joints between the gauze and the above-mentioned mask and metal frame. Therefore, the cleaning liquid remaining in the gaps at the adhesive joints may possibly cause a chemical change of the adhesive to loosen the fixation of the mask. Also, the remaining cleaning liquid may act on the ink with which management numbers or types of machine to be applied are printed on the mask or the metal frame, which will result in unclear indications. Masks molded with emulsion and the like other than the metal mask will also suffer from the same problems, that is, loosened fixation of the mask due to a chemical change caused by the remaining cleaning liquid, or unclear ink-printed indications.
The present invention was conceived to overcome the above problems which the conventional screen plate cleaning apparatus entails. It is therefore the object of the present invention t realize a compact and economical screen plate cleaning station with little or substantially no trouble, in which a zone to be necessarily cleaned on the screen plate is concentratedly cleaned to enhance the cleanability and the cleaning efficiency and in which the cleaning liquid is prevented from remaining in the gaps between the mask and the above-mentioned gauze and metal fame, with a simple structure.